Hesperian Health Guides

Managing Pests and Plant Diseases

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HealthWiki > A Community Guide to Environmental Health > Chapter 15: Sustainable Farming > Managing Pests and Plant Diseases

Pests, plant diseases, and weeds can be serious threats to crops. Chemical companies say the only solution is to spray pesticides regularly. But chemicals may cause more problems than they solve. Sustainable farming works with nature to keep crops, pests, diseases, weeds, and soil life in balance. This is called natural pest management or integrated pest management (IPM).

Natural pest management prevents problems with pests and plant diseases, and keeps harmful chemicals out of our bodies and environment. It also avoids problems of chemical dependence and pesticide resistance. (For some immediate methods to resolve pest problems, see “Spray with natural pesticides” and “Physical methods of pest control.”)

Even if you are willing to use pesticides, it is still important to know if pests are harming your crops, how much damage is being done, and whether creatures in the fields are already controlling the pest. Then you can decide if and when to use chemicals, and what kinds to use.

The best way to control both pests and diseases is to keep plants healthy.

  • Build healthy soil. Healthy soil provides a home to friendly insects and helps prevent many plant diseases.
  • Plant resistant varieties. Ask farmers or extension agents about seeds to make sure the ones you choose are resistant to common pests and diseases.
  • Space plants correctly. Planting crops too close together limits the sunshine and air that reaches the leaves, and allows diseases to thrive. But planting crops farther apart leaves room for weeds, dries the soil, and may reduce the harvest. Experiment to see what spacing works best for each crop.
  • Plant at the right times. Pests and diseases often respond to the weather, such as the first rains or the first warm day. Watching how each crop grows and talking with other farmers about these patterns can help you decide the best time to plant. Planting earlier than usual can make sure crops are big enough to resist pests or diseases that come at a certain time. Planting later can cause most of the pests or diseases to die out for lack of food.
Women tending different types of plants.
  • Plant a variety of crops and change crop patterns. Large areas with only 1 kind of plant attract pests who like that plant.
  • Water from below. Watering from above can cause diseases that live in soil to splash onto plants. And wet leaves and stems are good places for diseases to grow. Using drip irrigation or flood irrigation can keep plant leaves and stems healthy.

Look for pests

A man observes a caterpillar on a stalk of rice.
Watch what insects do to
see if they are damaging or
helping your crops.

Plant-eating insects are a normal part of farming. They cause little harm to crops as long as they remain in balance with other types of insects, especially those that eat pests.

Examine your crops regularly. This will help you understand when to allow friendly insects to do their work, and when you might need to spray with natural pesticides or use other pest control methods. When you look for pests and diseases, ask questions such as:

  • Are pieces of the plant being eaten by an insect?
  • Is damage increasing? Will it affect the crop yield?
  • Are friendly insects keeping pests under control?

Is it a pest, a friend, or harmless?

Sometimes the insects easiest to see are protecting plants by eating the pests. Or, the plant may be at a stage of growth where it can withstand some pest damage and remain healthy.

Worms are important for healthy soil. Bees, spiders, and most insects that live in water (such as in rice paddies) are friends, and help control pests. Also, small wasps or flies with long, thin tubes at their backside are probably friends. It is best to leave insect friends alone so they can help your crops.

Watch the insects in your fields to know if they are pests, friends, or harmless. If you are unsure about some insects, collect them in a container together with some plant parts, and watch them for several days. If you find insect eggs, watch what they hatch. If tiny worms or grubs (larva) are released, they may be pests. If they release flying insects, they are often friendly.

The main ways pests damage crops are by sucking the liquid from them and by eating them.

  • Sap-suckers include aphids, scale insects and mealy bugs, leaf and plant hoppers, white flies, thrips, mites, and nematodes.
  • Plant-eating insects include caterpillars, slugs, snails, plant and pod borers.

If it is a pest, how can you get rid of it?

Once you know how the pest damages crops, you can use natural pesticides made for that kind of pest.

Once you know when the pest appears and how it relates to its environment, you can use physical methods of pest control. Answers to these questions can help know how to control a pest: Where does it come from? When does it damage crops? Does it appear in one form and then change to another form (for instance, caterpillars turn into moths and butterflies)? Is it food for birds, other insects, or field creatures?

Spray with natural pesticides

Natural pesticides prevent crop damage with much less harm to people and the environment than chemical sprays. They are easy to make and cost less than chemicals.

But even natural pesticides must be used with care. Never use more than you need. Always wash your hands after handling them. Always wash food before eating or selling it. A natural pesticide may work well in some conditions but not in others. If one kind does not work, try other kinds.

Natural pesticides for plant-eating insects

Garlic, pepper, and chili pepper.
  1. Collect the plant you want to use, let it dry, and grind the dried plant to a powder.
  2. Soak the powder in water overnight (1 handful of powder to 1 liter of water).
  3. Pour the mixture through a screen or cloth to remove solids.
  4. Add a little bit of mild soap to help the pesticide stick to plants.
  5. Spray or sprinkle the mixture on plants. Test your mixture on 1 or 2 plants first. If it seems to hurt the plants, it may be too strong. Add more water and test it until it seems good.
  6. Repeat as needed, and after it rains.

Natural pesticides for sap-sucker insects

Sap-sucker insects are killed by coating them with mild soap or oil that blocks their breathing holes. Spraying plants with mild soapy water or water mixed with vegetable oil will kill these pests. Do not use detergents or strong soaps because they damage plants, soil, and insects.

Other natural pesticides

Urine diluted in water and sprayed on plants kills pests. Mix 1 cup of urine with 10 cups of water. Let it sit in a closed container for 10 days. After 10 days, spray the mixture onto your crops.

Tobacco kills many pests. Boil 1 cup of tobacco leaves or cigarette butts in 5 liters of water. Strain out the leaves or butts, add a little soap, and spray it on plants. Do not use tobacco on tomatoes, potatoes, peppers, and eggplant. It will damage these plants and will not kill most pests that attack them.

IMPORTANT! Tobacco juice is poison! Avoid getting tobacco juice on skin or clothes. Avoid breathing the steam while boiling tobacco leaves.

Physical methods of pest control

A bat, a bird, a frog, and a snake.
Watch the animals in your fields to know if they control pests.

There are many ways to control pests, or to encourage predators and parasites, based on their habits and life cycles. Talk to other farmers to learn about methods they use.

Animals and insects

Many birds, bats, snakes, and insects eat pests and pollinate crops. You can tell what a bird eats by the type of beak it has and by watching how it acts in your fields. To scare off birds that are eating crops, some farmers hang shiny things such as shiny paper, tape from old cassette tapes, and scraps of metal near crops.

Most bats eat mosquitoes. But some bats eat fruit and a few others bite animals. By watching them eat, or by looking at the remains of their food under the place where they sleep at night, you can tell if they are eating the fruit off your trees or are eating the insects that bite you or eat your crops.

Some physical methods of pest control

To control fruit flies, put some rotting fruit in a plastic bottle with fruit-fly-sized holes in it. Hang it from the fruit tree you want to protect about 6 weeks before the fruit will be ripe (when the flies start laying their eggs on the fruit). The flies will fly in but will not be able to get out.

Illustration of the below: a bottle hanging from a tree limb.
Make a few small holes in the bottle.
Fruit fly trap

Many small wasps feed on pollen and attack pests. Growing flowering plants that make lots of pollen will attract these wasps, and the wasps will protect crops from pests.

Tall trees planted around your field can stop locusts or make them pass over your field. Trees also provide shelter for useful insects.

Ants are fierce predators. If your crops are attacked by grubs, sprinkle sugar water on the stems or harvested tubers. Ants will come for the sugar water and stay to eat the grubs!

Many flying insects lay their eggs on crops. The eggs then hatch into grub and caterpillar pests. Hanging a torch or a lamp above a bucket or lined hole full of water will attract
flying insects, which then fall into the water and drown.
This solves the problem before any eggs can be laid or hatched.

Change crop patterns

Crops in the same plant family can get the same pests and diseases. For example, if you always plant potatoes in the same field, potato beetles may come to live and breed in that field. But if every 3 years you plant something they cannot eat, the beetles will leave or die. The third year crop must not be a relative of potato, like tomato or pepper. It should be something completely different, like maize. This is called crop rotation. 2 ways to prevent disease and pests are to rotate crops and to plant a variety of crops together.

Rotate crops

Rotating crops (changing the crops you grow in a particular field) controls diseases and pests by depriving them of food. It will also improve the soil by adding different nutrients. For example, rotating grains in one season with beans in the next will make the soil richer. Grains grow tall and provide organic matter, while beans add nitrogen to the soil.

Illustration of the below: trap plants.
Milk thistle plant
attracts harmful aphids.
Food crops nearby have few aphids.
Trap plants attract pests away from your crops.

Plant a variety of crops together

Planting different types of crops provides places for useful insects to live and makes it harder for pests to find the crop they like to eat. Growing many types of crops also improves food security, because if one crop fails, there are others to use. Planting different crops next to each other protects against pests in these ways:

  • Some strong smelling herbs and vegetables keep away pests.
  • Some flowers attract predators that eat pests.
  • Some plants “trap” pests. This is the opposite idea from keeping pests away. If you plant something that pests like better than your crop, they will stay on the “trap plant” and leave your crop alone.

Farmers also combine trees with animals and crops to increase the benefits of each of them.